a. Field of the Invention
The present invention relates to an optical fibre connector, for example an SC-style connector, and to a method of forming and using such a connector.
b. Related Art
The mechanical tolerances involved in terminating single mode optical fibre are much tighter than those for multimode optical fibre. Therefore, while it is quite common for multimode optical fibre be terminated at the point of use, for example at a user's premises or at an outside junction box, in most product applications, single mode optical fibre is not terminated in the field. When single mode fibre must be terminated in the field, then it can take a skilled technician between about 15 to 20 minutes to splice fibres together either by using a V-groove clamp or expensive fusion welding equipment.
Single mode fibre is therefore often provided in a range of different lengths, pre-terminated at both ends with a connector plug ready to plug into a matching receptacle. Commonly, eight or twelve single mode optical fibres may be bundled together in an optical fibre cable having an outer protective tube inside of which the optical fibres run.
An example of such a connector is the “Subscriber Connector”, or SC connector, originally developed by NTT®. SC connectors have convenient push/pull style mating, and are approximately square in cross-section and with a 2.5 mm diameter ferule at the termination of the optical fibre, surrounded by a plastic housing for protection. SC connectors are available in single or duplex configurations. The SC connector latches into a matching socket in a simple push motion. The push-pull design includes a spring against which the ferrule slides within a plastic inner housing. This arrangement provides a reliable contact pressure at the ferrule end and resists fibre end face contact damage of the optical fibre during connection. The connector can be quickly disconnected by first pulling back an outer housing, which is slidable relative to the inner housing, to disengage a latch inside socket between the socket and the inner housing, before pulling the optical fibre connector from the socket. Until the latch is thus disengaged, the latch prevents withdrawal of the connector when the optical fibre cable is pulled in a direction away from the socket.
A different type of connector is the ST type connector has a key that prevents rotation of the ceramic ferrule and which connects with a socket using a bayonet lock with an outer shell. All such bayonet type optical fibre connectors are referred to herein for convenience as “ST-type” optical fibre connectors.
An advantage of the SC connector over this type of bayonet connector is that the connector sockets can be more closely packed, as there is no need to get fingers fully around the connector to disengage the connector from the socket.
Other examples of push/pull type connectors are LC connectors or MU connectors. Often, the fibre-end is angled to reduce back reflections and this is usually described by adding APC (Angled Physical Contact) to the name. All such push/pull type optical fibre connectors are for convenience referred to herein as “SC-type” optical fibre connectors. SC-type LC or MU connectors are also known as small form factor connectors, by virtue of having a 1.5 mm diameter ferrule and a plastic housing.
It is important to avoid bending optical fibre around curves having too sharp a bend radius, as this will increase optical losses and can permanently damage the optical fibre. Optical fibre cables are therefore often routed inside a protective outer tube or conduit, which can have minimum bend-limiting properties. Protective bend limiting conduits normally have an outer diameter of 8 mm or 10 mm tubes. The cross-section of a standard SC connector has dimensions of about 7 mm×9 mm, and even a small form factor SC connector is too large to fit inside the inner diameter of a typical protective conduit.
In one product application involving the provision of a single mode optical connection all the way to a service subscriber, the protective conduit may run for tens or hundreds of meters from a residential home to a curb-side connection box. While it is relatively straight forward to blow or push a non-terminated length of optical fibre cable down the conduit, it is not possible to do this with cable pre-terminated with SC-type connectors owing to the mismatch in the size of the connector with the inner diameter of the conduit.
While, in principle, it would be possible to provide a length of optical cable pre-terminated at one end only, and then after blowing the cable down the conduit either splice or fuse the optical fibre to a terminated optical fibre stub, this adds significant time and cost to the job of providing a single mode optical fibre connection, particularly in product applications such as the provision of single mode optical fibre connection to a user's home.
It is an objection of the present invention to provide a more convenient optical fibre connector and optical fibre communication system and method for providing such a system.